The present invention relates generally to a backlight module, and in particular to a backlight module having a reduced weight while maintaining high luminance and uniform brightness throughout a light emitting surface thereof.
Backlight modules having reduced weight and minimized structure and size are known, such as Japan Patent Laid Open No. 21883/2001 which comprises two opposite glass plates between which polarizer, retarder, diffuser, color film, transparent electrode and liquid crystal layer are sequentially interposed. Corrugation is formed on the glass plate that faces a viewer for providing a front light.
Japan Patent Laid Open Nos. 00017/1990 and 84618/1990 disclose structures of planar light source, comprising a light guide plate having a light incident surface, a light emitting surface which is normal to the light incident surface and a light reflective surface that is opposite to the light incident surface and a light extraction mechanism forming a light source that is arranged on opposite ends of the light guide pipe. A light control sheet comprises a prism array disposed adjacent to the light emitting surface of the light guide pipe and comprising a number of triangular prisms having apexes pointing toward the light emitting surface of the light guide plate whereby a generating line of each prism is substantially parallel to the light source. A reflecting sheet is arranged adjacent to the light reflecting surface of the light guide plate.
Japan Patent Laid Open No. 84618/1990 teaches a technique for surface-roughing treatment of the light emitting surface of the light guide plate.
These prior art references provide techniques for projecting light in a given direction. However, they are not able to provide a uniform brightness throughout the light emitting surface. In addition, heretofore, the known planar light source devices are not able to provide wide viewing angles to be adapted in liquid crystal display or other thin thickness display devices, such as thin thickness television set.
On the other hand, the light source for a backlight module is commonly arranged on opposite ends of the backlight module. Light intensity from a light source comprised of a single light tube is sufficient to illuminate a light guide plate for liquid crystal display (LCD) panels having small sizes. However, for large sized LCD panels, a single tube light source is not able to provide uniform brightness throughout the whole panel. Additional light tubes are thus required to provide an acceptable brightness for illuminating the panel. FIGS. 1 and 2 of the attached drawings show conventional configurations for arrangement of more than one light tube in a light source for an LCD panel.
As shown in FIG. 1, a backlight module for a LCD panel comprises a light guide plate 2 and light sources 1 arranged on opposite ends of the light guide plate 2. Each light source 1 comprises three light tubes 10 lined up in a vertical direction or a direction normal to the LCD panel. Lining up three light tubes 10 inevitably increases the overall thickness A of the backlight module, which is against the trend of minimization. Practically, the thickness A of the backlight module having light source comprised of three tubes is around 10-13 mm.
In FIG. 2, a different arrangement of light tubes is shown. Two light sources 1, each comprised of three light tubes 12, 14, are arranged on opposite ends of a light guide plate 2. The light tubes 12, 14 are arranged in two columns and the tubes of each column alternate each other to reduce the overall thickness B of the backlight module. Practically, the thickness B is around 8 mm, which is substantially smaller than the technique illustrated in FIG. 1. However, the light tubes 14 that are arranged between the light tube 12 and the light guide plate 2 become obstacles for the light from the light tube 12 thereby causing loss of energy and reducing the luminance that can be provided by the backlight module.
Thus, it is desired to have a backlight module that overcomes the above problems.
An object of the present invention is to provide a backlight module that has sufficient and uniform brightness throughout a light emitting surface of a backlight module.
Another object of the present invention is to provide a backlight module that has reduced weight while maintaining a uniform and sufficient brightness.
A further object of the present invention is to provide a backlight module in which energy loss is eliminated or minimized.
To achieve the above objects, in accordance with the present invention, there is provided a backlight module comprising a light guide plate having opposite ends. The light guide plate has a light emitting surface and an opposite back surface connected to each other by the ends. The back surface has a concave contour whereby thickness of the light guide plate is gradually reduced from each end toward a center of the light guide plate. A light source comprises a reflector mounted to each end of the light guide plate and a plurality of light tubes fixed inside the reflector and between the reflector and the end of the light guide plate. The light tubes are lined up in a direction inclined with respect to a normal direction of the light emitting surface. The reflector comprises curved portions corresponding to the light tubes for reflecting light from the light tubes toward the end of the light guide plate. A reflective layer is formed on the back surface. The reflective layer defines a number of miniature cups having a hemispherical or multilateral pyramid configuration for reflecting light toward the light emitting surface.